1. Field of the Invention
The present invention relates to toner used in an image forming apparatus, such as a copying machine, a facsimile machine and a printer, and particularly in an image forming apparatus in which transfer of toner from a toner carrier toward a back electrode is controlled so that the toner adheres to an image receiving member, such as a transfer paper, a copying paper, a recording paper and a transfer medium, and an image is accordingly formed.
2. Description of the Related Art
Over the recent years, an image forming apparatus of the TonerJet (Registered trademark) method has attracted an increasing attention as an image forming apparatus which can be structured smaller at a lower cost than an apparatus of the electrophotographic method.
In this type of image forming apparatus, transfer of toner from a toner carrier to an image receiving member is controlled, the toner is made selectively adhere to the image receiving member at various positions and an image is accordingly formed. In short, electrified toner is rubbed against on the surface of the toner carrier and a toner layer is formed on the surface of the toner carrier, a potential difference is applied between the toner carrier and a back electrode and an electrostatic field for transfer accordingly develops which makes the electrified toner transfer toward the back electrode from the toner carrier. Disposed between the toner carrier and the back electrode is toner transfer controlling means which comprises a plurality of toner passing apertures and control electrodes which surround the respective toner passing apertures. As a voltage applied upon each control electrode is controlled in accordance with an image signal, each toner passing aperture is electrostatically opened and closed, the electrified toner is made transfer from the toner carrier toward the back electrode through the toner passing apertures in accordance with the image signal mentioned above, and the toner adheres to the image receiving member which is positioned between the toner transfer controlling means and the back electrode. In this manner, a toner image corresponding to the image signal is formed on the image receiving member.
In this type of image forming apparatus, it is in theory possible to form an image using toner whose property is approximately similar to that of such toner which is used in a conventional image forming apparatus by electrophotography. However, since these different types of image forming apparatuses are different from each other in terms of structure and operation principle, there are slightly different quality requirements regarding toner to be used in these image forming apparatuses. Hence, when toner developed for a conventional image forming apparatus is used in an image forming apparatus of the TonerJet method, a satisfactory image quality may not be always obtained.
For instance, in an apparatus of the TonerJet method wherein a member such as a toner regulating blade is disposed in contact with a toner carrier for the purpose of electrifying the toner and restricting the thickness of toner layer, a filming phenomenon may occur that friction-induced heat development, pressing force and the like make toner particles fuse to the surface of the toner carrier. As filming occurs at the surface of the toner carrier, the toner can not stay uniformly on the toner carrier, and therefore, the density of an image becomes uneven, a toner image fails to be formed at a necessary position or other image defect is created.
In addition, as described later, in this type of image forming apparatus, a spacer is used widely to keep the gap constant between a toner carrier and toner transfer controlling means. In such an apparatus, filming may occur at the spacer as well as at the toner carrier. Since the spacer is disposed in contact with the toner layer, friction occurs between the spacer and the toner layer, which may make a portion of the toner forming the toner layer fuse to the surface of the spacer or may make the toner fusing to the toner carrier contact with the spacer and stick to the spacer due to filming. If such filming at the spacer occurs, the toner layer may get damaged or the gap may change, thereby deteriorating the quality of an image. Thus, it is necessary to consider filming not only at the toner carrier but filming at the spacer as well.
Further, for example, since toner transferring from the toner carrier always passes through the toner passing apertures, the transferring toner may partially adhere to the toner transfer controlling means and clog the toner passing apertures. In this case, the density of a toner image formed on the image receiving member degrades, printing becomes impossible or other image defects occur.
In order to form a toner image having an excellent image quality with an image forming apparatus to the TonerJet method, therefore, toner whose property is suitable to apparatuses of this method is desired.